NORFOLK, Va. (Nick Ochsner, WVEC-TV, Hampton-Norfolk, Va.) — More questions are being raised about a Homeland Security ID program in wake of Monday's shooting at Naval Station Norfolk.

The suspect, 35-year-old Jeffrey T. Savage, used a valid Transportation Worker Identification Credential to gain unauthorized access to the world's largest naval base, the Navy has said. After he got on base, the truck driver passed through other layers of security, headed to the guided-missile destroyer USS Mahan, disarmed a sentry and killed a military policeman before being killed himself.

The Portsmouth, Va., resident was able to obtain his card, which contains his personal and biometric information, despite two felony convictions. He had to pass a Transportation Security Administration threat assessment check.

In 1998, Savage was convicted in federal court in Virginia for possession with intent to distribute crack cocaine, and in 2008 he pleaded guilty to voluntary manslaughter in North Carolina.

"Something went dreadfully wrong. In the 21st century era where there's very sophisticated notification systems, this kind of tragedy shouldn't be taking place," said Sen. Mark Warner, D-Va., who sent a letter Friday to Homeland Security Secretary Jeh Johnson and Navy Secretary Ray Mabus calling for answers about the process used to hand out the transportation credentials.

Warner's letter listed five questions for the two secretaries and pointed out a string of reports from the Government Accountability Office, which found major security flaws and other concerns in the TWIC program.

"The men and women who serve and put themselves in harm's way ought to be able to go to work when they're home ported and feel safe," Warner said. Master-at-Arms 2nd Class Mark Mayo, 24, of Hagerstown, Md., died at about 11:20 p.m. ET Monday when he responded to the commotion as chief of the guard for the USS Mahan.

The TWIC program was created after Sept. 11, 2001, as a way to strengthen security at commercial ports and other sensitive areas. The cards are commonly issued to truck drivers, employees of the Navy Military Sealift Command, merchant mariners and other employees who work at a commercial port.

Savage was incarcerated in various Virginia jails and North Carolina prisons for almost four years after being arrested in November 2005 in connection with the death of a man found shot to death on an interstate on ramp in Charlotte, N.C.

Savage, then 26, was driving with Maurice Griffin, 30, from Georgia to Virginia when they fought over a gun. Savage shot Griffin and left his body on the roadside.

Court records say prosecutors had planned to seek the death penalty against Savage if he didn't settle his case with a guilty plea. He was released from prison in December 2009.

Previously, Savage had spent nearly five years in a federal prison in Maryland on the drug charge and returned to a federal penitentiary for two more years when a judge in 2010 revoked his supervised release related to the drug charge.

Transportation Security Administration guidelines do not prohibit convicted felons from obtaining TWIC cards, but they are not eligible to get for the credential within five years of being released from prison on a felony charge.

Applicants who don't meet the eligibility requirements can apply for a waiver. The federal agency does not provide a list of criteria considered when deciding whether or not to grant a waiver to a felon.

"It's a big problem, and we're very troubled by it — very, very concerned about it," said Rep. Randy Forbes, R-Va.

Forbes, a member of the House Armed Services Committee, said he is following the investigation into Monday's shooting closely.

"He still should not have been on the facility at that time because he didn't have a work order or anything that needed to be in complement with that," Forbes said. "That's one of the things I think the investigation will turn up ... whether or not everybody was doing their job along the way."

Though the Navy's investigation into the shooting deaths is continuing, it has opened up a second investigation into improving security at the base, where about 46,000 service members and 21,000 civilian government employees and contractors serve.

That Savage was able to pass a security check after his two felony convictions and time in prison is troubling, homeland security expert Ed Clark said.

"I don't know what criteria they use" for waivers, Clark said when asked whether Savage should have been granted a waiver. "But I would say, the face value of that, probably not."